Having shown the superiority of Melchizedek to Abraham and Levi, the writer proceeded to point out the superiority of Melchizedek's priesthood and Jesus' priesthood. He did so to clarify for his readers the inferiority of the Mosaic Covenant and its priesthood. Not only was Melchizedek greaterthan Aaron, but Melchizedek replacedAaron.
"Within the structure of the homily, 7:1-28 is clearly defined as a literary unit. The reference to the Son of God' in v 3 prepares for the climactic reference to the Son' in v 28. The entire chapter is concerned with the Son as priest, or high priest, like Melchizedek,' who is superior to the Levitical priests. The fact that v 28 summarizes and concludes the comparison of Jesus as Son with the Levitical priesthood, a subject that occupies the writer in a preparatory way in 7:1-10 and directly in 7:11-28, is of special importance . . ."218
Genesis 14:17-20 now falls into the background, and Psalm 110:4 becomes dominant.219Note also the key words "perfection"(v. 11) and "perfect"(vv. 19, 28). These two words not only form an inclusiobut begin and end the argument of the pericope. Perfection did not come through the Old Covenant priests but through the Son.
Why would God replace the Levitical priesthood? Four reasons follow.